This invention relates generally to controlling the flow of production fluid in a well, and more particularly concerns apparatus and method to achieve surface control of a sub-surface valve, and independently of the pressure of production fluid in the well.
In the past, production flow controlling sleeve valves have been constructed to take advantage of the pressure of the production flow to urge the valve sleeve in one direction between open and closed positions. While this was in certain instances satisfactory, serious problems can arise when the pressure of the production flow varies, as for example can occur with the valve at a fixed installation depth, and also when the valve is moved up or down in the well. For example, if the production flow pressure increases greatly, then it requires much more control pressure to overcome the effect of increased production flow pressure on the valve sleeve, in order to shift the valve sleeve in the opposite direction, or to maintain the valve in open condition, for example. This condition in turn serves to limit the depths at which said sleeve type safety valves can be usefully installed, and also requires monitoring of such valves and adjustment of control pressure application to make sure that they remain in desired open or closed state.